What does the term "heterozygous" refer to?

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The term "heterozygous" refers specifically to an organism that has two different alleles for a particular trait. In genetics, alleles are variants of a gene that arise by mutation and are found at the same place on a chromosome. When an organism is heterozygous for a trait, it means one allele is inherited from one parent, and a different allele is inherited from the other parent. This genetic variation can influence the organism’s phenotype, or physical traits, because the different alleles may lead to different expressions of the trait.

For example, consider a trait governed by a single gene that has two alleles: one for brown eyes and another for blue eyes. If an organism receives one allele for brown eyes and one for blue eyes, it is heterozygous for that eye color trait. The dominant allele will often dictate the observable characteristic expressed, so in this case, the organism will likely have brown eyes.

Understanding heterozygosity is essential in the study of inheritance patterns, as it is a key factor in whether traits are dominant or recessive and how they may be passed on to offspring.